Canada's largest English daily newspaper publisher has had its credit rating cut over concerns it might not be able to pay back its debt.

Standard & Poor's analyst David Fisher said Postmedia's capital structure is "unsustainable," given the company's high interest costs and falling revenue from print newspapers.

The ratings agency said Postmedia could have trouble paying its debts within two years.

"The company could experience challenges refinancing its maturing debt starting in August 2017 ... due to secular pressure on print revenues," S&P said.

S&P has downgraded Postmedia Network's long-term corporate credit rating from a B- to CCC+— the same assigned to Greece.

The ratings service said it believes Postmedia has enough money to cover its costs "over at least the next 12 months," but that the situation is uncertain beyond that.

Postmedia, which owns and operates newspapers like the Ottawa Citizen, Calgary Herald and Edmonton Journal, has struggled with declining circulation and advertising revenues in the past. The company also recently scrapped its evening tablet edition, which it had hoped would bring in a new wave of digital journalism.

Despite a net loss of $263.4 million last year, CEO Paul Godfrey enjoyed a pay increase from $1.4 to $1.7 million, marking the second time he's made more money while Postmedia lost it.